Backlogged sediment can’t be allowed to build up forever, said John Dorney, wetlands and stormwater program development supervisor for the N.C. Division of Water Quality in Raleigh.
“It becomes one big mud flat,” Dorney said.
But Duke Energy District Manager Fred Alexander disputes that Duke will be made to dredge sediment from the lake.
“Let me be perfectly clear. We are NOT dredging Lake Emory,” Alexander said in an email response to The Smoky Mountain News.
Alexander said that Duke may do some “limited sediment removal,” but not a comprehensive dredging of the entire lake.
“That is not in our plans, nor a regulatory requirement,” Alexander said.
Yet according to a state water quality permit, how much sediment Duke will have to remove is not yet determined.
Duke is being required to develop sediment management plans for dams on the Oconaluftee River in Swain County and on the Hiwassee in Clay County. All three are known as “run-of-the-river” dams, where the respective dam transforms the river behind it into slow-moving backwater — more so than a bona fide lake. Lake Emory, located near Franklin, is 174 acres in size.
The state Division of Water Quality mandated that Duke address sediment removal as a condition of the water quality permits issued for all the three dams in summer of 2010.
“It could be one thing they have to do is dredge,” Dorney said.
The same requirements are being copied verbatim into the federal licenses for the dams being issued by the Federal Energy Regulatory Commission. Once issued, Duke “will absolutely have to develop a sediment management plan,” said Mark Cantrell, a biologist with the U.S. Fish and Wildlife Service. “FERC indicated Duke would need to include some management and not just monitoring — and that could include dredging.”
With Duke’s license for the dam up for renewal, that opened the door for new sediment rules to be imposed. And state and federal environmental agencies walked right in.
In short, Duke must conduct a sediment pilot study at one of the three dams, and a long-term sediment management plan after that. Cantrell said once the license was issued, it would trigger the sediment management plan within approximately the next six months.
Dorney knows Duke needs to do something about the mounting sediment behind the dams, but exactly what that should be — how much should be removed, how often, by what means — is up in the air pending the pilot study.
“We just didn’t know enough about how big the problems are and how fast they are developing and what mechanisms could solve the problems,” Dorney said. “The pilot study will get us that additional information.”
Dorney foresees Duke being made to remove some sediment from above Porter Bend Dam one way or another, however.
“That is the intent,” Dorney said.
And there’s only two ways to do that: dredge or flush it downstream.
When Duke tore down the Dillsboro dam, it lobbied hard for the “flushing” option. It argued that simply flushing the estimated 100,000 cubic yards of sediment downstream a bit at a time wouldn’t hurt the environment. It was also the cheaper of the two options. Ultimately, however, state and federal environmental agencies made Duke excavate much of the sediment (more than 63,000 cubic yards) from behind the dam rather than flushing it.
Dorney said it is too early for Duke to say whether it will or won’t dredge Lake Emory; and, he said, Duke isn’t the one that gets to decide that.
“They would have to say at this point they don’t know if they will have to do any dredging pending the results of the pilot study,” Dorney said.
The decision ultimately rests with the state and federal environmental agencies overseeing the water quality permits for the dam operations.
At stake is one of the most unique stretches of river in the eastern U.S., 13 miles of the Little Tennessee River, essentially unpolluted, uncontaminated and undeveloped.
“It is really incredible,” Cantrell said.
Which means there will be a whole lot of eyes watching as Duke develops a sedimentation management plan.
Dorney said in his view, it isn’t good for every grain of sediment in the river to get blocked by the dam.
“There is some concern about the river being sediment starved downstream from the dams,” Dorney said.
That may mean flushing some sediment downstream periodically.
“If they release some, that would get it out of the lake of course, but if you release too much it would destroy downstream, so it is a balancing act,” Dorney said.
There is only one caveat that would tip the scale against sediment removal, and one that just might come into play in Lake Emory.
Industrial pollution downstream from Lake Emory could have accumulated in the sediment over the years, and stirring it up could be bad news, according to water quality advocates with the Little Tennessee Watershed Association. (see related article.)
Dorney said that is definitely an area that needs more research, but doubts it would be a deal killer.
“If they did the studies and determined there would be more damage to the environment by removing it than leaving it there,” Dorney said. “But that isn’t likely.”
More often, the contaminants would be leaching out anyway, so removing them is still the best option.
Cantrell said toxic muck is “a legitimate concern.” He said there are detailed studies under way by Western Carolina University to try and pinpoint why there’s been a mussel-population decline below Lake Emory.
Cantrell said there are measurements that are indicating excessive levels of copper and other metals in Lake Emory, “and we are concerned about that being transmitted downstream.”By Becky Johnson and Quintin Ellison